Montana Field Guide

This Group is a minor type in Montana where it reaches its northerly extent in and around the Pryor Mountains. Communities are dominated by open stands of Utah Juniper (Juniperus osteosperma). Communities that are co-dominated by Limber Pine or Rocky Mtn Juniper with Utah Juniper are part of G209. Sites that contain Utah Juniper with Douglas-fir are generally part of the Pseudotsuga menziesii/Juniperus osteosperma Forest Communities (CEGL000440), which are part of G215.

This Group includes communities included in the Rocky Mountain Foothill Limber Pine - Juniper Woodland Ecological System.

Xeric, Conifer Woodlands; Wyoming and Bighorn Basins; Pryor Mtns.

Typical Dominants: Utah Juniper (Juniperus osteosperma)

In Montana, this Group is restricted to a relatively small geographic area that includes the lower elevations of the Pryor Mtns and surrounding areas where Utah Juniper reaches its northern extent.

In Montana, G105 occurs in Level IV Ecoregions: 17m (Dry Mid-elevation Sedimentary Mountains of the Middle Rockies), 18b (Bighorn Basin), and 43v (Pryor-Bighorn Foothills of the Northwestern Great Plains).

In Montana, G105 occurs or potentially occurs within these Major Land Resource Areas: 32 - Northern Intermountain Desertic Basins; southern part of 46 - Northern and Central Rocky Mountain Foothills.

Small Patch

These communities occur on the lower slopes and foothills of the Pryor Mountains. Elevations of these sites are mostly between 4,000-6,000ft and occur most commonly on southerly and westerly slopes or on dry, rocky ridgelines. Soils are generally shallow and derived from limestone or calcareous sandstone. Rock and gravel often cover >50% of the ground surface and bare soil is often as high as 20% or more. Soil subgroups include Ustic Torriorthents, Lithic Ustic Torriorthents, Lithic Ustollic Haplargids, and Ustollic Calciorthids. Surface textures varied from loam, sandy loam to silty clay with pH values from 7.4 to 8.0, and conductivity ranged from 200 to 310 uhmos/cm2 (DeVelice and Lesica 1993). Annual precipitation ranges from about 12-18 inches. Spring and early summer rainfall accounts for two-thirds of the annual precipitation (Knight et al. 1987).

Utah Juniper (Juniperus osteosperma) forms the overstory dominant at these sites. Adjacent sites may be dominated by Limber Pine (Pinus flexilis) or Rocky Mountain Juniper (Juniperus scopulorum) and these species may be present in Utah Juniper Woodlands as well. Low shrubs are often present, including Big Sagebrush (Artemisia tridentata), Low Sagebrush (Artemisia arbuscula), Black Sagebrush (Artemisia nova), Curl-leaf Mountain-Mahogany (Cercocarpus ledifolius) and Broom Snakeweed (Gutierrezia sarothrae). Common herbaceous species include grasses such as Bluebunch Wheatgrass (Elymus spicatus), Purple Threeawn (Aristida purpurea), Sandberg’s Bluegrass (Poa secunda), Prairie Junegrass (Koeleria macrantha), Indian Ricegrass (Oryzopsis hymennoides) and Bottlebrush Squirrel-tail (Elymus elymoides). Threadleaf Sedge (Carex filifolia) is also present at many sites. Forb diversity is often high though coverage is low. Common species include Allium textile, Arenaria hookeri, Milkvetches (Astragalus spp), Cryptantha spp, Fleabanes (Erigeron spp), Buckwheats (Eriogonum spp), Goldenweed (Stenotus acaulis), Ipomopsis spicata, Penstemon spp, Phlox spp, and Woolly Groundsel (Senecio canus). Plains Pricklypear (Opuntia polyacantha) is also present at many sites.

DeVelice and Lesica (1993) described 3 primary Utah Juniper Community Types from the Pryor Mountains. These are the Juniperus osteosperma/Agropyron spicatum c.t. with two phases (Gutierrezia sarothrae and Artemisia nova); the Juniperus osteosperma/Artemisia tridentata c.t.; and the Juniperus osteosperma/Cercocarpus ledifolius c.t. with two potential phases (Artemisia nova phase on deeper soils and the nearly barren Agropyron spicatum (Elymus spicatus)) phase on shallow soils. The Juniperus osteosperma/Cercocarpus ledifolius c.t. was reported to cover 1990 acres and the Juniperus osteosperma/Artemisia tridentata c.t. 670 acres (Lesica 1994).

Alliances and Associations for this group in Montana likely need additional review as only one of each is currently attributed to the state, while DeVelice and Lesica (1993) described 3 primary Utah Juniper Community Types from the Pryor Mountains.

Junipers are slow-growing, long-lived trees (about 650 years for Juniperus osteosperma and 300 years for Juniperus scopulorum) (Burns and Honkala 1990a, Zlatnik 1999e, Scher 2002, Sawyer et al. 2009). Fires in these woodlands are thought to be infrequent because Utah Juniper and many shrubs such as Big Sagebrush are easily killed by burns and do not resprout (Barney and Frischknecht 1974, Everett 1986). In addition, many stands have an open canopy with insufficient understory to carry fire. Shrubs will often re-establish relatively quickly (about 10-20 years) if a seed source is nearby (Barney and Frischknecht 1974, Bunting 1987). However, Utah Juniper is relatively slow to recover following fire, and shrubs such as sagebrush may dominate the sites for decades (Jameson et al. 1962). Fire, drought and competition with grasses are thought to have kept Juniper communities restricted to rocky areas that do not burn frequently (Wright et al. 1979). There has been significant expansion of these woodlands over the last century into sagebrush-dominated shrublands. An altered fire regime (such as fire suppression, thus longer return intervals) is considered a primary cause of this expansion. Invasion by Cheatgrass (Bromus tectorum) commonly occurs within arid environments including Juniper woodlands and has the potential to alter fire regimes by providing a fine, continuous fuel layer that was previously absent at these sites.

K. Schulz; Triepke et al. (2021)